/Engine/Source/Runtime/Engine/Classes/Engine/World.h
Given a PackageName and a prefix type, get back to the original package name (i.e. the saved map name)
static [FString](API\Runtime\Core\Containers\FString) StripPIEPrefixFromPackageName ( const [FString](API\Runtime\Core\Containers\FString) & PackageName, const [FString](API\Runtime\Core\Containers\FString) & Prefix )